The Supreme Court agreed today to step into the racially charged debate over whether a key section of a nearly 50-year-old federal voting law that Congress enacted to stop racial discrimination at the polls is still warranted.

The justices announced that they would take up a case brought by Shelby County, Ala., challenging Section 5 of the 1965 Voting Rights Act. The provision, the county argues, is unconstitutional because it requires select state and local governments in designated states, but not others, to submit proposed changes to their voting laws to the Justice Department for approval, or preclearance, before they can go into effect.

All or parts of 16 states — mainly in the South with a history of racial discrimination in elections — are currently subject to the provision. All others can and do enact voting changes without federal approval. Shelby County argues that the distinction is unfair because it is based on a decades-old formula that Congress devised to test whether states might be using discriminatory practices, but which no longer reflects reality in the states subject to oversight.

When Congress reauthorized the Voting Rights Act six years ago, it did so with broad bipartisan support as both Democrats and Republicans hailed the legislation as historic and effective in preventing discrimination at the polls.

The court’s decision to examine a central feature of the law is certain to have reverberations in Congress, particularly amid growing partisanship in the institution and in the states over the voting rights of minorities.

The court’s involvement also could force Congress to respond with legislation, depending on how the justices eventually rule. The court could, for example, strike down the current formula for determining which states are subject to federal oversight and leave it to Congress to come up with a new formula.

Specifically, the county argues, Congress overstepped its constitutional authority when it renewed the Voting Rights Act, including Section 5, for an additional 25 years in 2006. Congress did so without making any effort to determine whether the affected states still deserve to face the burden of Justice Department scrutiny of their voting laws, lawyers contend.

“Congress held not one hearing, proposed not one bill and amended not one law” despite growing evidence that those states may no longer deserve to be singled out, the lawyers for the county argue, asking the court to intervene because of congressional inaction.

While the court did not set a date for oral arguments in the case, Shelby County v. Holder, the challenge will be heard sometime after mid-January, with a decision likely before the justices adjourn in late June.